This invention relates generally to processes for assembling hand tools. More specifically, the present invention relates to closed back shovels and to a novel process for manufacturing such shovel heads and attaching them to the ends of composite handles.
In manufacturing handles for hand tools such as shovels, rakes and the like, competing design considerations are at play. On the one hand it is desirable to have a handle that is as light as possible, to provide for easy use by consumers. On the other hand the handle must have the structural integrity to withstand the variety of stresses that will be placed on it. Wooden handles have been used, but these provide an unacceptable compromise of weight for structural integrity.
An alternative to wooden handles is the use of rods formed from resin coated fibers. The basic technique for running filaments through a resin bath and then into a long heated die tube to produce a cured composite of the same shape as the die tube has been known for some time. See, for example, U.S. Pat. Nos. 2,948,649 and 3,556,888. This method, however, produces a solid extruded product which is unacceptably heavy and/or too costly.
The weight problem can be alleviated by means of an existing process to extrude hollow tubes utilizing a die tube with the center filled, leaving an annular cross-section through which the fibers are pulled. However, this weight reduction is achieved at the cost of significantly lower tensile and compression (bending) strength than that of a solid rod, and therefore would not be suitable for use in certain high-stress applications such as general purpose shovel handles. Further, to increase interlaminar strength, a substantial percentage of fibers running other than in a longitudinal direction may be required. Moreover, commercial machines for producing continuous hollow tubing are extremely expensive.
As illustrated and described in U.S. Pat. Nos. 4,570,988 and 4,605,254 (the contents of which are incorporated herein by reference), the bending strength of tool handles can be improved by producing rods which are substantially hollow or lightweight throughout most of their length, but reinforced at areas of expected increased stresses. Typically, one of the areas to be reinforced in a hand tool is at the front end, where the attachment between the tool head and the handle is effected.
Many hand tools such as hoes, cultivators, rakes and the like, are provided with tangs or an elongated piece of metal which is part of the tool head and is used traditionally to attach the tool head to a wooden handle. There are millions of such tool heads in existence which may be reused with replacement tool handles. To attach such tanged tool heads to composite handles, typically a bore is provided in the front end of the composite tool handle having a diameter larger than the cross-sectional dimensions of the tang itself. The tang is attached to the composite rod by bonding or chemically adhering the tang within the bore. This process, however, has been found to be unacceptably costly and time consuming, and not well suited for field replacement of wooden tool handles.
Problems have also been encountered in the attachment of composite tool handles to socketed tool heads, such as shovel blades, as described in U.S. Pat. No. Re. 32,364. A large percentage of shovel blades are made by starting with a sheet steel blank, and stamping out the configuration of a shovel with the appropriate shape for a digging portion, the socket, and the structural stiffening sections. The traditional process of forming a shovel blade creates a substantial back-side cavity or hollowed-out area between the end of the shovel socket and approximately the center of the blade. This cavity or recess is very undesirable in anything but the cheapest shovels, as it is prone to collect dirt, clay, mud or other materials during use, which adds substantially to the weight of the shovel.
To eliminate or substantially reduce this back-side cavity, shovel blades are modified into what is called a closed back (as opposed to an open back) configuration. This is accomplished by means of welding a roughly triangular steel plate over the cavity. This process increases the costs associated with manufacturing a closed back shovel blade, since there is an additional ten to fifteen inches of welding, slag cleaning, and further re-heat treating or annealing of the shovel blade to eliminate brittle spots caused by the welding process.
To accommodate the decreasing strength of available wood handle materials, the length of the blade socket of most shovels has grown over the years. Much of the material utilized for the socket can be eliminated as wasteful, however, when a superior strength composite handle is utilized in place of wood. In the past, however, composite-type handles have been attached to the shovel blade by means of a screw, rivet or the like, which mechanically attaches the front end of the tool handle to the shovel socket. In some limited instances, even this method of attachment can undesirably degrade the overall strength and working characteristics of the tool handle.
Accordingly, there has been a need for a novel process for manufacturing closed back shovels and for attaching such shovel heads to ends of composite handles which simplifies prior processes, eliminates the waiting time associated with bonding processes, and facilitates the rapid assembly of closed back shovels to increase manufacturing cost efficiencies. Such an assembly process must provide a means for securely holding the tool head relative to the handle under all anticipated working conditions. Additionally, a novel assembly process is needed which can be utilized to quickly and efficiently create a closed back shovel simultaneously with attaching the composite handle to a standard open back shovel blade. Moreover, a closed back shovel is needed which eliminates the prior requirement of welding a plate over the back-side cavity of the shovel blade, and the increased manufacturing costs associated therewith. The present invention fulfills these needs and provides other related advantages.